The map function applies a user supplied transformation function to
each element in a list, returning a new list containing the
transformed elements.
This module provides a 'parallel map'. Multiple worker processes are forked so
that many instances of the transformation function may be executed
simultaneously.
For time consuming operations, particularly operations that spend most of their
time waiting for I/O, this is a big performance win. It also provides a simple
idiom to make effective use of multi CPU systems.